I use 25G/0.5" for delts and bis and i use 23G/1" for glutes and thighs. These are probably as small as most will want to go… and even skinny lads could use the sizes i mentioned.
NB: I could easily use 1" for delts/bi and 1.5" for glute/quad but it isnt necessary, as i know that 0.5-1" is going to be deep enough with my bodyfat level. Even if i had ronnies musculature, with a decent bodyfat 0.5" is still enough of a depot depth for biceps.
I most commonly use 1ml and 2ml barrels - When injecting less than 1ml per dose i use the lower volume barrel, when more - i use the higher volume!
It is not an exact science - generally one uses the shorter needles for the lower fat areas and the thinner needles for the smaller muscle groups - and anything wider than 23G is unnecessary for any AAS based product IME.
21G is totally fine for oil and is actually referred to as an Oil-Pipe in some anabolic circles, however it is just going to cause more damage when the 23G would have worked fine. I have used the 21G on many occasions and have no scar tissue to note, but i choose differently these days.
It will take longer to draw from an amp or vial with a smaller gauge - but so the fuck what? If it is really an issue due to time restraints when jacking up in a Burger King (oh, wrong forum…:/) then draw with a green or yellow (21G and 19G respectively) and shoot with a lower gauge.
As someone noted above, the pressures created with the smaller barrels is more than enough to squirt the gear through a very low gauge (upto 29G IIRC - but not 31G IME) - so with this new information it would be cunning to load with a 23G or so, and shoot with a fresh 25-29G, avoiding any further unnecessary tissue damage)
Also worth mentioning… an 18G is not going to be much of an issue with a 10ml multi in regards to damaging the rubber stopper (as does happen with repeated use) as it is discarded after that, but why you would use an 18G for anything in our interests (other than brewing purposes) is beyond me.
For simplicity it is no more difficult than sticking to the first 2 lines of this post.
Hope this helps.
This has to be the end of the thread?!